velesdb-core 1.7.0

//! Vacuum and compaction operations for `ColumnStore`.
//!
//! Extracted from `mod.rs` for maintainability (04-06 module splitting).
//! Handles tombstone removal, column compaction, and deletion bitmap operations.

use super::types::{TypedColumn, VacuumConfig, VacuumStats};
use super::ColumnStore;

use roaring::RoaringBitmap;
use std::collections::HashMap;

/// Filters a column vector, removing entries at deleted indices and counting reclaimed bytes.
fn compact_vec<T: Copy>(
    data: &[T],
    deleted: &rustc_hash::FxHashSet<usize>,
    element_bytes: u64,
) -> (Vec<T>, u64) {
    let mut new_data = Vec::with_capacity(data.len().saturating_sub(deleted.len()));
    let mut bytes_reclaimed = 0u64;
    for (idx, value) in data.iter().enumerate() {
        if deleted.contains(&idx) {
            bytes_reclaimed += element_bytes;
        } else {
            new_data.push(*value);
        }
    }
    (new_data, bytes_reclaimed)
}

impl ColumnStore {
    /// Runs vacuum to remove tombstones and compact data.
    ///
    /// This operation removes deleted rows from the column store, reclaiming
    /// space and improving query performance. The operation is done in-place
    /// by building new column vectors without the deleted rows.
    ///
    /// # Arguments
    ///
    /// * `_config` - Vacuum configuration (batch_size, sync options)
    ///
    /// # Returns
    ///
    /// Statistics about the vacuum operation.
    pub fn vacuum(&mut self, _config: VacuumConfig) -> VacuumStats {
        let start = std::time::Instant::now();
        let tombstones_found = self.deleted_rows.len();

        if tombstones_found == 0 {
            return VacuumStats {
                tombstones_found: 0,
                completed: true,
                duration_ms: start.elapsed().as_millis() as u64,
                ..Default::default()
            };
        }

        let mut stats = VacuumStats {
            tombstones_found,
            ..Default::default()
        };

        let (old_to_new, new_row_count) = self.build_compaction_map();
        self.compact_all_columns(&mut stats);
        self.remap_primary_index(&old_to_new);
        self.remap_row_expiry(&old_to_new);

        stats.tombstones_removed = self.deleted_rows.len();
        self.deleted_rows.clear();
        self.deletion_bitmap.clear();
        self.row_count = new_row_count;

        stats.completed = true;
        stats.duration_ms = start.elapsed().as_millis() as u64;
        stats
    }

    /// Builds the old-to-new row index mapping, skipping deleted rows.
    fn build_compaction_map(&self) -> (HashMap<usize, usize>, usize) {
        let mut old_to_new: HashMap<usize, usize> = HashMap::new();
        let mut new_idx = 0;
        for old_idx in 0..self.row_count {
            if !self.deleted_rows.contains(&old_idx) {
                old_to_new.insert(old_idx, new_idx);
                new_idx += 1;
            }
        }
        (old_to_new, new_idx)
    }

    /// Compacts all columns, removing deleted rows and accumulating reclaimed bytes.
    fn compact_all_columns(&mut self, stats: &mut VacuumStats) {
        for column in self.columns.values_mut() {
            let (new_col, bytes) = Self::compact_column(column, &self.deleted_rows);
            stats.bytes_reclaimed += bytes;
            *column = new_col;
        }
    }

    /// Remaps the primary index to use compacted row indices.
    fn remap_primary_index(&mut self, old_to_new: &HashMap<usize, usize>) {
        if self.primary_key_column.is_none() {
            return;
        }
        let mut new_primary_index: HashMap<i64, usize> = HashMap::new();
        let mut new_row_idx_to_pk: HashMap<usize, i64> = HashMap::new();
        for (pk, old_idx) in &self.primary_index {
            if let Some(&new_idx) = old_to_new.get(old_idx) {
                new_primary_index.insert(*pk, new_idx);
                new_row_idx_to_pk.insert(new_idx, *pk);
            }
        }
        self.primary_index = new_primary_index;
        self.row_idx_to_pk = new_row_idx_to_pk;
    }

    /// Remaps row expiry timestamps to compacted row indices.
    fn remap_row_expiry(&mut self, old_to_new: &HashMap<usize, usize>) {
        let mut new_row_expiry: HashMap<usize, u64> = HashMap::new();
        for (old_idx, expiry) in &self.row_expiry {
            if let Some(&new_idx) = old_to_new.get(old_idx) {
                new_row_expiry.insert(new_idx, *expiry);
            }
        }
        self.row_expiry = new_row_expiry;
    }

    /// Compacts a single column by removing deleted rows.
    fn compact_column(
        column: &TypedColumn,
        deleted: &rustc_hash::FxHashSet<usize>,
    ) -> (TypedColumn, u64) {
        match column {
            TypedColumn::Int(data) => {
                let (new_data, bytes) = compact_vec(data, deleted, 8);
                (TypedColumn::Int(new_data), bytes)
            }
            TypedColumn::Float(data) => {
                let (new_data, bytes) = compact_vec(data, deleted, 8);
                (TypedColumn::Float(new_data), bytes)
            }
            TypedColumn::String(data) => {
                let (new_data, bytes) = compact_vec(data, deleted, 4);
                (TypedColumn::String(new_data), bytes)
            }
            TypedColumn::Bool(data) => {
                let (new_data, bytes) = compact_vec(data, deleted, 1);
                (TypedColumn::Bool(new_data), bytes)
            }
        }
    }

    /// Returns whether vacuum is recommended based on tombstone ratio.
    ///
    /// # Arguments
    ///
    /// * `threshold` - Ratio of deleted rows to trigger vacuum (0.0-1.0)
    #[must_use]
    pub fn should_vacuum(&self, threshold: f64) -> bool {
        if self.row_count == 0 {
            return false;
        }
        let ratio = self.deleted_rows.len() as f64 / self.row_count as f64;
        ratio >= threshold
    }

    // =========================================================================
    // EPIC-043 US-002: RoaringBitmap Filtering
    // =========================================================================

    /// Checks if a row is deleted using RoaringBitmap (O(1) lookup).
    ///
    /// This is faster than FxHashSet for large deletion sets.
    #[must_use]
    #[inline]
    pub fn is_row_deleted_bitmap(&self, row_idx: usize) -> bool {
        if let Ok(idx) = u32::try_from(row_idx) {
            self.deletion_bitmap.contains(idx)
        } else {
            // Fallback to FxHashSet for indices > u32::MAX
            self.deleted_rows.contains(&row_idx)
        }
    }

    /// Returns an iterator over live (non-deleted) row indices.
    ///
    /// Uses RoaringBitmap for efficient filtering.
    pub fn live_row_indices(&self) -> impl Iterator<Item = usize> + '_ {
        (0..self.row_count).filter(|&idx| !self.is_row_deleted_bitmap(idx))
    }

    /// Returns the deletion bitmap for advanced filtering operations.
    #[must_use]
    pub fn deletion_bitmap(&self) -> &RoaringBitmap {
        &self.deletion_bitmap
    }

    /// Returns the number of deleted rows using the bitmap (O(1)).
    #[must_use]
    pub fn deleted_count_bitmap(&self) -> u64 {
        self.deletion_bitmap.len()
    }
}